MITOGENIC STIMULATION OF HUMAN-LYMPHOCYTES MEDIATED BY A CELL-SURFACEELASTASE

A ca, 45-kDa protein which was recently identified and purified to hom ogeneity from a solid tumor cell line as a T-cell mitogen was found to have significant sequence similarities with human monocyte/neutrophil elastase inhibitor (EI) [1]. Since EI is a known substrate for elasta se, a determination of whether a cell surface expressed elastase-like molecule might be the binding protein for this 45-kDa factor and media te mitogenic signal transduction was undertaken. First, the surface of tumor infiltrating lymphocytes, TIL 660. the indicator cell line used for the purification of this mitogen, was shown to stain positively w ith an anti-elastase antibody using flow cytofluorometry for quantitat ion. Then, after observing an inverse correlation between cell surface staining and the proliferative status of the TILs, behavior which mig ht be expected of a growth factor receptor upon activation, mitogenic signal transduction was attempted through the elastase-like molecules of the lymphocytes' plasma membrane with the anti-elastase antibody in the role of mitogen, A greater than 4-fold mitogenic stimulation was observed when this antibody was covalently linked to latex beads; in c ontrast, addition of the soluble form of the same antibody did not res ult in any increase in [H-3]thymidine incorporation into the cells' DN A. Hence, these data support induced clustering of an elastase-like mo lecule on the lymphocyte surface as a mediator of mitogenesis and sugg est that the binding protein for mitogenic signal transduction induced by the 45-kDa protein, a member of the serine protease inhibitor (ser pin) superfamily of proteins, is a molecule with structure similar to a serine protease.